Keratin: It is a strong non-soluble fibrous protein that makes up hair, nails, and skin. See related article on Hair Care

Ketamine: A dissociative anesthetic similar to PCP. Used mainly in veterinary medicine due to it's causing "out of body" experiences in humans. Street names include: Special K, K, Ket, Smack K, Kit-Kat, and others.

Kleptomania: The overwhelming and persistent desire to steal even though it is not for monetary gain.